Title

Author

Date of Award

Degree Type

Open Access Thesis

Document Type

Master Thesis

Degree Name

Master of Science (MS)

Department

Biological Sciences

First Advisor

David R. Brown

Department Affiliation

Biological Sciences

Abstract

White-throated sparrows (Zonotrichia albicollis) are songbirds that spend the non-breeding season in southeastern North America, where they form philopatric territorial flocks. Flocks exhibit dominance hierarchies, with dominance rank associated with an individual's age and prior residence in the territory. Although social behaviors within flocks are well studied, few studies have described winter home ranges. I tagged white-throated sparrows (n = 12) in Madison County, Kentucky, with 0.9-g radio transmitters during the winter of 2010-2011. Locations were entered into ArcGIS and home range sizes were estimated with 50% and 95% kernel analysis for individuals with at least five locations. Mean core home ranges were 1.59 ± 0.3 (SD) ha, and 95% home ranges averaged 5.31 ± 0.8 ha. Core home ranges were significantly larger than estimates from previous studies. Differences among locations in food abundance and distribution may explain variation in home range sizes.

During the winter of 2011-2012, I focused on behavioral aspects of wintering sparrows. Flocks use distinct territories and maintain their ranked relationships throughout the winter, though familiarity lessens outright conflict as the season progresses. White-throated sparrows, unlike most songbirds, continue singing throughout winter and likely become accustomed to the songs of other flock members. I examined the responses of resident flocks to unfamiliar individuals and vocalizations throughout the winter, while also examining circulating levels of the stress hormone, corticosterone, to see if they paralleled behavioral changes. Concurrently, I validated identification of sparrow plumage morphs with genotype assays to determine reliability of field identification. I mounted study skins of white-throated sparrows 1 m above ground and played randomly selected 10-minute tracks of songs and chips interspersed with silence during three discrete periods during the (November, January, and March). Responses and agonistic behaviors were noted; plasma samples were collected concurrently to measure corticosterone. Accuracy of field identification of plumage morphs was 68.8%. Baseline corticosterone did not differ among sampling periods, suggesting these birds did not experience prolonged chronic stress throughout the winter. However, white-throated sparrows responded more aggressively to study skins and playback of conspecific calls and songs in November than in January and March. These results suggest that agonistic displays may be more important for defending winter territories and establishing dominance status in early winter.